A ring network including a plurality of nodes provided as communication apparatuses that are coupled in a ring-like manner has been achieved as one of network connection configurations. The data forwarding technology of Ethernet (Registered Trademark) can be applied for the ring network. In that case, data is forwarded between the nodes as a frame of Ethernet. The ring network which allows for efficient wiring by establishing links between the nodes has often been used as a wide-area network.
The failure recovery technology referred to as ring protection has been used as a technology relating to the ring network. The ring protection system is stipulated in, for example, International Telecommunication Union-Telecommunication standardization sector (ITU-T) Recommendation G.8032.
According to the ring protection system stipulated in ITU-T Recommendation G.8032, one of the nodes that are provided on the ring network is specified as a master node. The master node includes a blocking port (BP) which does not let a frame pass there through to avoid the frame circulation. When a failure occurs in a certain link in that state, failure notification-message data is forwarded between the nodes. Upon receiving the failure notification-message data, the master node opens the BP to let the frame pass there through. Accordingly, a forwarding route which allows for detouring round the link where the failure occurs is ensured. Here, according to ITU-T Recommendation G.8032, a frame forwarded in a connectionless manner is the object to be protected.
Further, the ring network may include an end-to-end path so that a frame is forwarded over the path corresponding to path identification information added to the frame. The above-described data forwarding method can be achieved by using, for example, the virtual local area network (VLAN) technology of Ethernet. The path identification information may be a VLAN identifier, a pair of the VLAN identifier and a media access control (MAC) address, etc. In that case, each of the nodes that are provided on the ring network performs the frame switching based on the path identification information, which indicates that each of the nodes may not learn the address of the frame.
As a technology relating to failure recovery performed in the ring network, providing a route used when a failure occurs in a ring part and that used when a failure occurs in a connection part in a compatible and harmonious manner in a system including two ring networks that are coupled to each other via a plurality of the connection parts has been proposed (see paragraph [0015] of Japanese Unexamined Patent Application Publication No. 2002-232442, for example).